1. Field of the Invention
The field of this invention relates to crystalline copolyamides from terephthalic acid and mixtures of hexamethylenediamine and trimethylhexamethylenediamine.
2. Background
Crystalline copolyamides from terephthalic acid and mixtures of hexamethylenediamine and trimethylhexamethylenediamine have not been obtained in the prior art. In fact, U.S. Pat. No. 3,382,216 teaches that the preparation of polyhexamethylene terephthalamide cannot be effected through melt condensation processes. U.S. Pat. No. 3,150,117 discloses that linear amorphous film forming polyamides can be prepared from dicarboxylic acids and alkyl-substituted saturated hydrocarbons such as trimethylhexamethylenediamine; hexamethylenediamine is not disclosed in this reference. Other pertinent references include U.S. Pat. No. 3,294,758, which discloses that compositions containing greater than 30 percent hexamethylenediamine are brittle. U.S. Pat. Nos. 3,825,516; 3,962,400; 3,294,758; 2,846,379 and 4,250,297 disclose amorphous polyamides. In reviewing all these references, it is clear that the crystalline polyterephthalamides manufactured from terephthalic acid and mixtures of hexamethylenediamine and trimethylhexamethylenediamine including filled compositions of these polymers having a heat deflection temperature of about 240.degree. to about 305.degree. C. are unknown in the prior art.
The general object of this invention is to provide crystalline polyterephthalamides and molding compositions reinforced with glass fibers, glass beads, minerals, graphite fibers or a mixture thereof. We have now found that crystalline polyterephthalamides can be obtained from terephthalic acid (TA) and a mixture of hexamethylenediamine (HMDA) and trimethylhexamethylenediamine (TMHMDA). The mole ratio of HMDA and TMHMDA can vary from about 55/45 to about 98/2, preferably about 60/40 to about 95/5. This crystalline polymer, when filled and molded with glass fibers, glass beads, minerals, graphite fibers or a mixture thereof, usually has a heat deflection temperature of at least about 240.degree. C. to about 305.degree. C., as determined by ASTM method D648. This is an unusual feature and completely unexpected, since amorphous polyterephthalamides have much lower heat deflection temperatures. The importance of having high heat deflection temperatures is that it enables the injection molded polyterephthalamides to be used in applications such as the hood of an automobile, shroud for a lawn mower, chain saw guard, and electrical connector applications. Our molded compositions have good mechanical properties such as tensile strength, flexural properties and impact strength.
The molecular weight of our copolyamides is about 5,000 to about 40,000. Our novel composition can be filled with about 10 to about 60 weight percent glass fibers, glass beads, minerals, graphite fibers, or a mixture thereof. Advantageously, the molding composition may contain from about 20 to about 50 weight percent of glass fibers, glass beads, minerals, graphite fibers, or a mixture thereof. Our studies have shown that high heat deflection temperatures are obtained and the cost of molding products derived from polyterephthalamides are reduced by substituting for part of the polymer about 20 to about 50 weight percent thereof with glass fibers, glass beads, minerals, or graphite fibers. These glass filled polyamides and copolyamides are much more economical than molding compositions prepared without the use of the glass fibers, glass beads, minerals, or graphite fibers. Novel fibers can also be prepared from the polyamide and copolyamide derived from polyterephthalamide and this is indicated by the excellent physical properties of these polyamides.
Our novel crystalline polyterephthalamides are suitably extruded at a temperature of about 300.degree. to about 350.degree. C. through a fiber die having a multiplicity of apertures of about 0.06 inch diameter each. Fiber strands are suitably taken up at about 10 to about 1200 meters per minute, preferably at about 500 to about 1000 meters per minute. The fibers are suitably taken at a temperature of at least about 300.degree. C., advantageously, in the range of about 320.degree. to about 350.degree. C., preferably, in the temperature range of about 330.degree. to about 340.degree. C. to give fibers having a tenacity of about 5 grams per denier and an initial modulus of about 25 grams per denier. The use of polyimides and amides as engineering plastics has been limited only by their relatively high cost. Thus, employing our invention, through which the inherent cost can be brought down, the commercial application of polyamides requiring very high heat deflection temperatures can be greatly expanded.
We have prepared monofilaments using our novel polyamide. With monofilament, the process starts with a single screw extruder to supply a melt for conversion to fiber. The die for monofilament is similar to the multifilament die. The monofilament is a slower operation process, typically about 50 to about 200 feet/minute. For the melt spinning operations about 40 to about 80 feet/minute were used for the monofilament processing. The monofilament, on the other hand, is water quenched with much less melt draw down. The monofilament is subsequently drawn with heated drawing systems. The monofilament drawing is done in-line using heated ovens.
TABLE 1 ______________________________________ Copolyamide Monofilament ______________________________________ Melt Sample T.sub.m Temp Denier Elongation TA/HMDA/TMHMDA (.degree.C.) (.degree.C.) (g/9000m) (%) ______________________________________ 100-50/50 707 25.5 100-60/40 310 .about.330 613 10.1 ______________________________________ Initial Draw Sample Tenacity Modulus Ratio TA/HMDA/TMHMDA (g/d) (g/d) (X:1.0) ______________________________________ 100-50/50 3.3 46.8 100-60/40 5.4 65.2 4.5 ______________________________________
Suitably, in our process for the manufacture of polyterephthalamides, the reaction temperature is kept in the range of about 260.degree. to about 315.degree. C. and HMDA and TMHMDA, in the mole ratio of about 55/45 to about 95/5, preferably in the mole ratio of about 60/40 to about 90/10, are reacted without the addition of any external solvent. The reactant melt temperature in our process is kept in the range of about 250.degree. to about 270.degree. C. In the preferred process, the reaction is conducted in a Helicone reactor, preheated to a temperature of about 90.degree. to about 150.degree. C. In our process for the manufacture of polyamides, about equal molar amounts of TA are reacted with a primary aliphatic diamine, such as HMDA and TMHMDA. The molar ratio of TA to the aliphatic primary diamine may be in the range of about 1.2:1 to about 1:1.2, preferably in the range of about 1:1.
Our novel injection moldable crystalline polyamide copolymer of HMDA and TMHMDA comprises the following recurring structural units: ##STR1## wherein R is a straight chain aliphatic hydrocarbon radical containing 6 carbon atoms and R' is an alkyl-substituted saturated hydrocarbon chain, 6 carbon atoms in length in which the alkyl substitution comprises 3 methyl groups with two of the three methyl groups on the same carbon atom. The preferred alkyl-substituted diamines for our novel compositions are 2,2,4-trimethylhexamethylenediamine and 2,4,4-trimethylhexamethylenediamine or mixtures of these. Injection molding of our polyterephthalamide, filled or unfilled, is accomplished by injecting the polyamide into a mold maintained at a temperature of about 100.degree. to about 200.degree. C. In this process, a 20 second to 1 minute cycle is used with a barrel temperature of about 300.degree. to about 350.degree. C. These temperatures will vary depending on the glass transition temperature (Tg) and melt temperature (Tm) of the polyamide being molded. The Tg and Tm of our polyterephthalamide are about 120.degree. to about 160.degree. C. and about 300.degree. to about 340.degree. C., respectively. The polyterephthalamide has excellent thermal and mechanical properties and can readily be molded into useful products or formed into fibers, laminates or coatings. The physical properties of the claimed polyamide are disclosed in Table 3. The Tg of this polyamide is 149.degree. C. and the Tm is about 315.degree. to about 320.degree. C.
We have found that the polyterephthalamide of this invention is improved by the addition of reinforcing materials; particularly, the thermal properties are improved if the polyterephthalamide contains from about 10 to about 60 percent by weight glass fibers, glass beads, minerals, graphite fibers, or mixtures thereof. In the preferred range, the polyterephthalamides contain about 20 to about 50 percent by weight of the glass fibers, glass beads, minerals, graphite fibers, or mixtures thereof. Suitably, the reinforcing materials can be glass fibers, glass beads, glass spheres, or glass fabrics. The glass fibers are made of alkali-free boron-silicate glass or alkali-containing C-glass. The thickness of the fibers is suitably on the average between 3 microns and 30 microns. It is possible to use both long fibers in the range of from 5 to 50 mm and also short fibers with each filament length of 0.05 to 5 mm. In principle, any standard commercial grade fibers, especially glass fibers, may be used. Glass beads ranging from 5 microns to 50 microns in diameter may also be used as a reinforcing material.
The reinforced polyamide polymers may be prepared in various ways. For example, so-called roving, endless glass fiber strands, are coated with the polyamide melt and subsequently granulated. The cut fibers or the glass beads may also be mixed with granulated polyamide and the resulting mixture melted in a conventional extruder, or, alternatively, the fibers may be directly introduced into the polyamide melt through a suitable inlet in the extruder. Injection molding of the novel glass filled polyamide is achieved by injecting the polyamide into a mold maintained at a temperature of about 100.degree. to about 200.degree. C. In this process, a 40 second cycle is used with a barrel temperature of about 300.degree. to about 350.degree. C. The injection molding conditions are given in Table 2.
TABLE 2 ______________________________________ Mold Temperature 100.degree. to 200.degree. C. Injection Pressure 6,000 to 15,000 psi and held for 10 to 20 seconds Back Pressure 100 to 1,000 psi Cycle Time 20 to 60 seconds Extruder: 320.degree. to 340.degree. C. Nozzle Temperature Barrels: 300.degree. to 350.degree. C. Front Heated to Screw: 20 to 60 revolutions/minute ______________________________________
Catalyst can suitably be employed in our process. These catalysts include the following compounds: NaH.sub.2 PO.sub.2, H.sub.3 PO.sub.2, H.sub.3 PO.sub.4, H.sub.2 SO.sub.4, HCl, Na.sub.3 PO.sub.3, NaH.sub.2 PO.sub.4.H.sub.2 O. The amount of catalyst present can vary from about 0.01 to about 0.2 weight percent of the total weight of the reactants. The preferred catalyst is sodium hypophosphite.